N-(3-ethynylphenyl)maleimide

ABSTRACT

Acetylene terminated aspartimides are prepared using two methods. In the first, an amino-substituted aromatic acetylene is reacted with an aromatic bismaleimide in a solvent of glacial acetic acid and/or m-cresol. In the second method, an aromatic diamine is reacted with an ethynyl containing maleimide, such as N-(3-ethynylphenyl)maleimide, in a solvent of glacial acetic acid and/or m-cresol. In addition, acetylene terminated aspartimides are blended with various acetylene terminated oligomers and polymers to yield composite materials exhibiting improved mechanical properties.

ORIGIN OF THE INVENTION

The invention described herein was jointly made by employees of theUnited States Government and contract employees in the performance ofwork under a NASA Contract and Grant and is subject to the provisions ofPublic Law 96-517 (35 USC 202) in which the contractor has elected notto retain title and/or the provisions of Section 305 of the NationalAeronautics and Space Act of 1958, as amended, Public Law 85-568 (72Stat. 435; 42 USC 2457).

CROSS-REFERENCE TO RELATED APPLICATION

The application is a division of U.S. patent application Ser. No.328,392, filed Mar. 24, 1989, which is now U.S. Pat. No. 4,889,912,which is a continuation-in-part of U.S. patent application Ser. No.087,375, filed Aug. 20, 1987, abandoned.

BACKGROUND OF THE INVENTION

Structural resins with a favorable combination of properties such aslong term environmental durability over a temperature range of -54° to220° C., damage tolerance, and solvent resistance are required for usein hot areas on military and commercial aircraft. Commercially availablebismaleimide resins such as Compimide 353 (available fromBoots/Technochemie) and XU-292 (available from Ciba/Geigy Corporation)previously have been formulated with other components to enhanceproperties such as melt processability and toughness. These formulatedsystems have found use in a variety of applications such as compositematrices and adhesives for use at temperatures in excess of those atwhich epoxy systems can perform.

Polyaspartimides are commonly synthesized by reaction of aromaticbismaleimides with aromatic diamines. These polymers have a repeat unitof the following general formula: ##STR1## where Ar and Ar' are divalentaromatic radicals, such as 1,3-phenylene or 4,4'-oxydiphenylene.

High molecular weight polyaspartimides are known [J. V. Crivello, J.Polymer Sci., 11, 1185(1973)] and can form tough, flexible films withgood tensile properties and can be compression molded. However,uncrosslinked polyaspartimides are susceptible to solvent attack,especially in a stressed condition, and upon exposure undergo solventinduced stress crazing and cracking. In addition, polyaspartimides aregenerally soluble in dipolar solvents such as N,N-dimethylformamide,dimethyl sulfoxide, N,N-dimethylacetamide, N-methylpyrrolidinone,phenol, and m-cresol. Melt condensation of aromatic diamines andbismaleimides has been reported to yield cross-linked polymers(polyaspartimides) [F. Grundschober and J. Sambeth (To Soc. Rhodiacita),U.S. Pat. No. 3,533,996 (Oct. 13, 1970)].

In most cases, less than a stoichiometric amount of an aromatic diamineis reacted with a bismaleimide to yield a low or intermediate molecularweight polyaspartimide terminated with maleimide groups. Upon heating,the terminal maleimide groups react to yield a crosslinked resin havingless toughness than the linear polyaspartimides but with improvedsolvent resistance and higher use temperature. The degree ofcrosslinking can be controlled to a large extent by the stoichiometry. Acommon material of this type is Kerimid 601 (available from RhonePoulenc), used extensively in printed circuit boards.

The acetylene terminated aspartimides (ATA) of this invention presentnew compositions of matter. The properties of cured acetylene terminatedaspartimides are similar to those of the cured unformulatedbismaleimides but they have significantly higher toughness. In addition,the acetylene terminated aspartimides are formed as stereoisomers (d, land meso isomers), and as such have lower melt temperatures thanbismaleimides with similar chemical structure. Since they are a mixtureof isomers, they also melt over a broad temperature range. Both of thesefactors make acetylene terminated aspartimides more amenable to processinto adhesive tape and prepreg via melt technique than comparablebismaleimides.

The acetylene terminated aspartimides can be readily blended withacetylene terminated arylene ether oligomers and polymers to yield curedresins with high toughness. The crosslink density can be controlled byvarying the ratio of acetylene terminated aspartimide to acetyleneterminated arylene ether oligomers or polymers and also by varying thelength and chemical structure of the linear segment in the acetyleneterminated arylene ether oligomers or polymers. The acetylene terminatedaspartimides can also be blended with acetylene terminated polysulfonesto yield resins with high fracture toughness.

Accordingly, it is an object of this invention to provide a method ofpreparing acetylene terminated aspartimides.

A further object of this invention is to provide acetylene terminatedaspartimides that are useful as adhesives, coatings, films and compositematrices.

A further object of the present invention is to provide blends ofacetylene terminated aspartimides and other acetylene terminatedoligomers and polymers that are useful as adhesives, coatings, films,membranes and composite matrices.

SUMMARY OF THE INVENTION

According to the present invention, the foregoing and additional objectswere attained by synthesizing aspartimide oligomers and polymerscontaining terminal acetylene groups. Acetylene terminated aspartimideswere prepared using two methods. In the first, an amino-substitutedaromatic acetylene was reacted with an aromatic bismaleimide in asolvent of glacial acetic acid and/or m-cresol. In the second method, anaromatic diamine as reacted with an ethynyl containing maleimide, suchas N-(3-ethynylphenyl) maleimide, in a solvent of glacial acetic acidand/or m-cresol. In addition, acetylene terminated aspartimides wereblended with various acetylene terminated oligomers and polymers toyield composite materials exhibiting improved mechanical properties.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprehends synthesizing acetylene terminatedaspartimides using two methods. In the first, an amino-substitutedaromatic acetylene is reacted with an aromatic bismaleimide. The generalreaction sequence is represented by the following equation: ##STR2##where x is selected from a group of radicals consisting of nil, CH₂, O,S, C═O, SO₂, C(CH₃)₂, C(CF₃)₂, ##STR3## and mixtures thereof. Linkage ofthe bismaleimide may be para, para; meta, meta; or meta, para. Anyaromatic amine containing a terminal acetylenic group such as3-aminophenylacetylene or 4-aminophenylacetylene may be used. Any polarsolvent may be used. Particularly beneficial results were obtained usingglacial acetic acid or m-cresol containing a small amount of glacialacetic acid.

The aromatic bismaleimide may be a maleimide-terminated polyaryleneether oligomer. This oligomer may be prepared by reaction of anaminophenol such as 4-aminophenyl-4'-hydroxyphenyl-2,2-propane with theappropriate amounts of a diphenol and an activated dihaloketone in orderto produce an amine-terminated polyarylene ether oligomer. This diaminooligomer may then be converted to the bismaleimide by reaction withmaleic anhydride followed by cyclodehydration. ##STR4##

Alternately, the maleimide-terminated polyarylene ether oligomers can bemade in one step by the reaction of compounds such as ##STR5## with theappropriate amounts of diphenol and activated dihalo compound.

In the second method, acetylene terminated aspartimides are prepared byreacting an aromatic diamine with an ethynyl containing maleimide. Thegeneral reaction sequence is represented by the following equation:##STR6## where x is selected from a group of radicals consisting of nil,CH₂, O, S, C═O, SO₂, C(CH₃)₂, C(CF₃)₂, ##STR7## and mixtures thereof.Linkage of the diamine may be para, para; meta meta; or meta, para. Anyethynyl containing maleimide such as N-(3-ethynylphenyl) maleimide orN-(4-ethynylphenyl) maleimide may be used. As in method 1 any of variouspolar solvents may be used.

The aromatic diamine may be an amine-terminated polyarylene etheroligomer as previously described for the first method.

The present invention further comprehends novel composite materialsformed by blending acetylene terminated aspartimides with variousacetylene termined polymers. The acetylene terminated aspartimide fromthe reaction of 3-aminophenylacetylene andN,N'-bismaleimido-4,4'-diphenylmethane was blended with an equal weightof an acetylene terminated sulfone oligomer (the number of averagemolecular weight of the sulfone segment was approximately 9000 g/mole).Such oligomers have the following general formula: ##STR8## where n isan integer from 3 to 59. The resulting blend was then processed andcured at a maximum temperature range of 230°-250° C. A molded specimenprepared therefrom showed a significant improvement in fracturetoughness with a K_(Ic) (stress intensity factor) of approximately 1400psi.in^(1/2) compared to unblended acetylene terminated aspartimides.This specimen was not affected upon exposure to methylene chloride orother solvents. A 30% solids solution of the blend in methylene chloridewas used to impregnate carbon/graphite fabric. The prepreg was stackedand cured in an autoclave by holding at 149° C. for 20 minutes and at177° C. for two hours under 80 psi. The composite was postcured in apress at 232° C. for one hour under 100 psi to give a final compositewith a calculated resin content of approximately 41%. At 25° C.,flexural strength, flexural modulus, and short beam shear strengths weredetermined to be 93,500 psi, 7,575,000 psi, and 8600 psi, respectively.At 177° C., the respective values were 87,800 psi, 6,266,000 psi, and7200 psi.

The invention is not limited to this example of blends of the acetyleneterminated aspartimides with sulfone oligomers but includes blends invarying proportions of the acetylene terminated aspartimides with allacetylene terminated polyarylene ethers of the following generalstructure which can be prepared according to a procedure similar to thatdisclosed in U.S. Pat. No. 4,431,761: ##STR9## wherein n is an integerrepresenting 3 to 60 repeat units. Linkage of the phenylethynyl groupsmay be either meta or para. Ar is a divalent aromatic radical selectedfrom the group consisting of: ##STR10## wherein X is selected from thegroup consisting of O═C and SO₂, and y is a bond, or is selected fromthe group consisting of O, S, CH₂, C═O, SO₂, C(CH₃)₂), and C(CF₃)₂, Ar'is a divalent aromatic radical selected from the group consisting of:##STR11## wherein X is a bond or a selected from the group: CH₂, O, S,C═O, SO₂, C(CH₃)₂, and C(CF₃)₂.

It should become obvious to those skilled in the art that this inventionis not limited to the examples herein described. Additionally, thisinvention includes blends of acetylene terminated aspartimides withacetylene terminated phenylquinoxaline oligomers, acetylene terminatedimide oligomers, acetylene terminated ester oligomers and various otheracetylene terminated oligomers.

EXAMPLES EXAMPLE I Synthesis of an ATA by reaction of3-aminophenylacetylene with N,N'-bismaleimido-4,4'-diphenylmethane.

A solution of N,N'-bismaleimido-4,4'-diphenylmethane (38.34 g, 0.10mole) and distilled 3-aminophenylacetylene 23.43 g, 0.20 mole) wasdissolved in 100 mL of m-cresol containing 4 ml glacial acetic acid. Theresulting solution was stirred under a nitrogen atmosphere with thetemperature of the reaction mixture maintained at 100°-110° C. for 48hours. The solvent was removed under vacuum and the residue dried undervacuum at 90° C. A nearly quantitative yield of light yellow solid wasobtained which was a mixture of d, l and meso isomers, mp 104°-110° C.The material resisted recrystallization but an analytically pure samplewas obtained by precipitation from a chloroform solution with methanol.Elemental analysis calculated for C₃₇ H₂₈ N₄ O₄ : C, 74.98%, H, 4.76%,N, 9.45%. Found: C, 75.04%, H, 4.93%; N, 9.29%. From differentialscanning calorimetry analysis (DSC) of this ATA, a melting endotherm wasdetected at 81° C. and an exothermic peak due to reaction of theacetylene groups was detected at 266° C. From thermogravimetric analysis(TGA) at a heating reate of 2.5° C. per minute, this ATA after curing at250° C. for one hour, exhibited 5% weight loss in air at 370° C. and innitrogen at 355° C. By isothermogravimetric analysis at 260° C. incirculating air, this cured ATA exhibited 17% weight loss after 110hours.

EXAMPLE II Synthesis of an ATA by Reaction ofN-(3-ethynylphenyl)maleimide with 4,4'-diaminodiphenylmethaneN-(3-ethynylphenyl)maleimide

Maleic anhydride (79.6 g, 0.81 mole) was added to a solution ofdistilled 3-aminophenylacetylene (95.1 g, 0.81 mole) dissolved in 500 mLof dry N,N'-dimethylacetamide (DMAc) at 5°-10° C. After addition,another 300 mL of DMAc was added and the mixture stirred at roomtemperature for two hours. Nickel acetate tetrahydrate (0.8 g) andacetic anhydride (300 mL) were added to the reaction mixture andstirring was continued for 12 hours at room temperature to affectcyclodehydration. The crude product was isolated by precipitation inwater and recrystallized from methanol to provideN-(3-ethynylphenyl)maleimide (128 g, 80% yield) as a yellow crystallinesolid, mp 129°-131° C. Elemental analysis calculated for C₁₂ H₇ NO₂ : C,73.09%; H, 3.58%; N, 7.10%. Found: C, 72.94%, H, 3.61%; N, 7.04%.

Acetylene Terminated Aspartimide (ATA)

N-(3-ethynylphenyl)maleimide (13.80 g, 0.070 mol) and4,4'-diaminodiphenylmethane (6.94 g, 0.035 mole) were dissolved in 200mL of glacial acetic acid and the solution heated to reflux for 24 hoursunder a nitrogen atmosphere. The solution was added to water toprecipitate the ATA as a light yellow solid in nearly quantitative yieldas a mixture of d, l and meso isomers, mp 110°-115° C. Elementalanalysis calculated for C₃₇ H₂₈ N₄ O₄ : C, 74.98%; H, 4.76%, N, 9.45%.Found: C, 74.81%, H, 4.80%; N, 9.38%. From differential scanningcalorimetric analysis of this ATA, a melting endotherm was detected at119° C. and an exothermic peak due to reaction of acetylene groupsdetected at 209° C. From thermogravimetric analysis, this ATA aftercuring at 300° C. for 15 minutes exhibited 5% weight loss in air at 385°C.

EXAMPLE III

Preparation of a 1:1 blend of the ATA prepared from the reaction of3-aminophenylacetylene with N,N'-bismaleimido-4,4'-diphenylmethane andan acetylene terminated sulfone oligomer (number average molecularweight of sulfone segment, 8890 g/mole).

The ATA from the reaction of 3-aminophenylacetylene withN,N'-bismaleimido-4,4'-diphenylmethane (50 g) and an acetyleneterminated sulfone oligomer (number average molecular weight of sulfonesegment, 8890 g/mole) (50 g) were dissolved in 200 mL of chloroform withwarming. The solution was mixed and the chloroform allowed to evaporate.The residue was crushed, allowed to air dry, and then dried under vacuumat 90° C. Solutions of this blend in 1,4-dioxane were used to coatadhesive specimens and methylene chloride solutions were used to preparecarbon-graphite prepreg. The blend can also be prepared directly in1,4-dioxane. For the preparation of moldings, the blend was prereactedat 200° C. for ten minutes in order to decrease melt flow. From TGA thisblend after curing at 250° C. for one hour exhibited 5% weight loss inair at 386° C. and in nitrogen at 392° C. By isothermogravimetricanalysis at 260° C. in circulating air, this cured blend exhibited 10%weight loss after 110 hours.

The invention is not limited to these examples.

What is claimed is:
 1. N-(3-ethynylphenyl)maleimide.